Dish reflector with detachable waveguide feed



J. J. GLYNN 3,483,564

DISH REFLECTOR WITH DETACHABLE WAVEGUIDE FEED Dec. 9, 1969 2Sheets-Sheet 1 Filed Got 17, 1966 INVENTOR JAMES J. GLYNN w ATTORNEYSDec. 9, 1969 J, J, NN 3,483,564

DISH REFLECTOR WITH DETACHABLE WAVEGUIDE FEED INVENTOR JAMES J. GLYNNATTORNEYS US. Cl. 343771 7 Claims ABSTRAQT 01*" THE DISCLOSURE Ashort-circuited waveguide illuminates a parabolic reflector from opposedslots in the broad walls adjacent to the short-circuiting plate. Thewaveguide is detachably secured to a reflector flange permanentlyattached to the reflector surface at a waveguide flange. The reflectorflange has studs with heads that fit through openings in the waveguideflange. A locking ring is formed with slotted openings that fit over thestuds and have a locking portion for gripping the underside of the studheads when the locking ring is in locked position to keep the waveguidesecured to the reflector.

The present invention relates in general to illuminating withelectromagnetic energy and more particularly concerns novel methods andmeans for illuminating a reflector with microwave energy over anexceptionally wide frequency range with compact structure characterizedby low windage, ease of assembly and adjustment, relatively low cost andquick connect-disconnect capabilities.

According to the invention, means are provided for supporting a lengthof waveguide from a reflector to be illuminated. Means are also providedfor terminating the waveguide in a conducting plate that extends beyondthe cross section of the waveguide in a plane substantially erpendicularto the waveguide axis. The waveguide wall is formed with aperturedefining .rneans closely adjacent to and generally parallel to theterminating conducting plate, thereby defining an electromagnetic energypath including the waveguide, the reflector and the aperture. Theterminating conducting plate may include means defining an adjustableconducting element penetrating into the waveguide to an adjustable depthin a direction generally parallel to the waveguide axis in the vicinityof the plane passing through the aperture means for matching theimpedance of the coacting combination of the aperture defining means andthe terminating conducting plate to the wave impedance of the waveguide.

Preferably the reflecting surface is defined by a conic section such asa parabola of revolution with the aperture means located substantiallyat the reflector focus. Preferably the waveguide is rectangular with itsaxis coinciding with the axis of symmetry of the reflector and withapertures symmetrically located in the opposed broad walls. Preferablythe conducting terminating plate is circular with its center embracingthe waveguide axis.

According to another feature of the invention there is a reflectorflange atached to the reflector for receiving a waveguide flange towhich the waveguide is secured. A locking ring is fastened to thewaveguide flange. The waveguide flange is formed with openingssupporting spring-loaded ball plungers that provide tension against thelocking ring when properly positioned in the reflector flange andrestrain the locking ring from rotating beyond the angle of detentsmachined in the locking ring.

For many years microwave systems have often employed reflectors,typically parabolic, with a suitable feed, such as a horn of Cutler typefeed located at the focus to form a radiating system characterized by adesired dinited States Patent rectivity pattern, typically highlydirectional. Such systems have a number of disadvantages. Bandwidth isrestricted. VSWR is less than that desired. Windage is relatively high.The moment of inertia is relatively high, a disadvantage of moreimportance When the reflector and feed assembly are rotated oroscillated to effect scanning.

Accordingly, it is an important object of this invention to overcome oneor more of the preceding disadvantages.

More specifically, it is an object of this invention to provide animproved feed means for association with a reflecting surfacecharacterized by relatively broad bandwidth, relatively low VSWR,relatively low moment of inertia, relatively low windage, relatively lowcost, relative ease of manufacture, and relative ease of adjustment toobtain optimum electrical performance.

It is another object of this invention to achieve one or more of thepreceding objects with a feed means that may be rapidly and easilyconnected or disconnected to facilitate assembly and disassembly in thefield and permit rapid substitution of different feeds for differentfrequencies.

Numerous other features, objects and advantages of the invention willbecome apparent from the following specification when read in connectionwith the accompanying drawing in which:

FIG. 1 is a side view, partially in diametrical section of an embodimentaccording to the invention;

FIG. 2 is a top view of the detachable feed system according to theinvention;

FIG. 3 is a view through section 3-3 of FIG. 2;

FIG. 4 is a side view of the asembly of FIG. 2;

FIG. 5 is an end view of the input flange secured to the Waveguide;

FIG. 6 is a front View of the terminating conducting plate;

FIG. 7 is a back view of the reflector flange where attached to thereflector; and

FIG. 8 is a view of the locking ring face.

With reference now to the drawing and more particularly FIG. 1 thereofthere is shown a side view, partially in diametrical section of areflector and feed system according to the invention. Since importantportions of the structure exhibit circular symmetry and top, side, frontand back views fully disclose the construction of a preferredembodiment, such views are shown in the drawing to best illustrate theprinciples of the invention. Energy from an upper aperture 11 and loweraperture 12 in upper broad wall 13 and lower broad wall 14,respectively, of waveguide 15 illuminates parabolic reflector 16 withenergy incident through waveguide input opening 17 of reflector flange21. Reflector flange 21 is shown permanently fastened to the central rim22 of reflector 16 by welding or other suitable mechanical techniques.Reflector flange 21 may be formed with a recess as shown foraccommodating a pressure window 23. Reflector flange 21 is alsopreferably formed with a channel 24 comprising a quarter wavelengthchoke.

Reflector flange 21 is also preferably formed with tapped openings, suchas 25, for accommodating a threaded stud, such as 26, that guideswaveguide flange 31 into nesting relationship in reflector flange 21 asillustrated. Waveguide flange 31 may also be formed with a recess foraccommodating a pressure window 32. Waveguide flange 31 includesopenings for accommodating studs, such as stud 26, and tapped holes foraccommodating retainer screws, such as 33. Waveguide flange 31 is formedwith an annular shoulder 34 for accommodating locking ring 35 that keepswaveguide flange 31 securely seated in reflector flange 21 by grippingthe heads of studs, such as stud 26, in a manner which will be betterunderstood from the discussion which follows.

Waveguide is preferably soldered or braised to waveguide flange 31 andterminates in a radiating section 36 with opposed narrow walls slightlynarrower than the narrow walls of the rest of the waveguide by exactlyone wall thickness. Radiating section 36 includes slits 11 and 12 inbroad walls 13 and 14 comprising aperture defining means and isterminated in conducting end plate 37. Conducting plate 37 includes anaxially located matching screw 41 with a lock nut 42 and may alsofunction to fasten circular end plate 37 to a cap placed over the end ofwaveguide section 36. It may be desirable to employ additional screwssuch as 61, 62 and 41 to achieve optimum matching. Slits 11 and 12preferably ha\e the dimensions indicated in fractions of air wavelengthat center frequency when covered by material having a dielectricconstant of the order of 2.2. Note that the slit width is much less thana quarter wavelength while the slit length is greater than a quarterwavelength and less than a half wavelength at the center frequency ofthe operating range.

Referring to FIG. 2, there is shown a top view of the detachablewaveguide feed assembly. Like reference symbols are used to identifycorresponding elements throughout the drawing. FIG. 2 also illustrates adetail of how one of the three unequiangularly spaced spring loaded ballplungers, like 43 in waveguide flange 31, detent lock in a matingrecess, such as 44 in locking ring 35.

Referring to FIG. 3, there is shown a view through section 33 of FIG. 2helpful in understanding how the quick connect-disconnect mechanismfunctions. Opposed screws 33 and 33 keep locking ring 35 secured towaveguide flange 31, prohibiting any substantial axial movement of thelocking ring while allowing angular movement through substantially 15degrees determined by the angular width of slots 51 and 52. Thisarrangement allows locking ring 35 to be rotated between unlock positionand the lock position shown in FIG. 3 in which locking studs 26, 26' and26" have their respective heads bearing against the beveled innersurface of slots 53, 54 and 55, respectively. Unlocking and locking isfacilitated by the diametrically opposed fingers 56 and 57. To unlockthe waveguide feed section it is only necessary to apply acounterlockwise. torque to fingers 56 and 57 until the clockwisemostportions of slots 53, 54 and 55 are aligned with the heads of studs 26,26 and 26". In this position, the three angularly spaced spring loadedballs lock in three corresponding detents, 44, 44 and 44", in lockingring 35, thus securing locking ring 35 in the remove or unlock position.Then grasping the waveguide feed assembly 15, it may be withdrawn fromthe reflector assembly because the heads of studs 26, 26' and 26" clearthe clockwisemost openings in slots 53, 54 and 55. The reverse procedureis practiced to quickly connect the waveguide feed assembly. That is,the assembler grasps fingers 56 and 57, aligns the clockwisernostopenings of slots 53, 54 and 55 over the heads of studs 26, 26 and 26",seats the assembly so that waveguide flange 31 is nested in reflectorflange 21 and then rotates fingers 56 and 57 clockwise until the threespring loaded ball plungers like 43 snap into a corresponding recesssuch as 44a, 44a and 44a" in locking ring 35, rapidly securing theassembly into position with a secure mechanical and electrical cou lingto the reflector assembly.

FIG. 8 illustrates the face of ring 35 showing recesses 44, 44' and 44"which facilitate maintaining the unlock position. Detent positions 44a,44a and 44a" are used to maintain the lock position.

Referring to FIG. 4, there is shown a side view of the waveguide feedassembly. Referring to FIG. 5, there is shown a back view of theassembly of FIG. 4 better illustrating the openings 53, 54' and 55through which screws 26, 26 and 26 pass when the waveguide assembly isnested in position and reflector flange 21 together With a view of theorientation of ball plungers 43, 43' and 43", respectively, in openings44, 44 and 44", respectively, of locking ring 35.

Referring to FIG. 6, there is shown a front View of terminatingconducting plate 37 showing screw 41 and locking nut 42. There is alsoshown two openings 61 and 62 along a line generally parallel to thebroad walls of the waveguide symmetrical about screw 41 foraccomomodating an additional pair of screws like 41 to help improve theimpedance match. Adjustment of screw 41 is accomplished by energizinginput 17 through impedance measuring means, such as a slotted waveguide,and adjusting screw 41 until a minimum VSWR is measured. To

allow for mechanical tolerances in production, provision for additionalscrews in openings 61 and 62 permits fine impedance matching for lowVSWR by screw adjustment at these points.

Referring to FIG. 7, there is shown an end view of the reflector flange21 showing the four tapped holes 63, 64, 65 and 66 for receiving screwsthat secure a mating flange from a rectangular waveguide that exchangesenergy with the invention and external transmitting and/ or receivingapparatus.

The invention has a number of electrical and mechanical advantages. Theoperating band width is of the order of 18% with a VSWR attainable ofless than 1.2. Exceptionally good illumination of the reflecting surfaceis obtained because the slits 11 and 12 closely approximate a pointsource centered substantially midway between the slits 11 and 12 withconducting plate 37 imaging slits 11 and 12 into virtual sources thatconfine almost all the energy emitted from slots 11 and 12 to impingingupon reflector 16. To this end it is preferable that the angle ofradiated energy beyond the axis of the waveguide 15 containsapproximately of the power available to illuminate the parabolicreflector, and this angle corresponds substantially with the anglesubtended by the axis and periphery, measured from the focus. Reflectorplate 37 diameter is chosen to satisfy the above criteria.

The structure is relatively easy and inexpensive to fabricate,lightweight, rugged and characterized by relatively low windage andmoment of inertia because the only structure in addition to thewaveguide is conducting plate 37 and the tuning screws, and theseelements extend only slightly beyond the distance for the reflector 16to the focus. And the quick connect-disconnect feature facilitates rapidassembly and disassembly, even under severe combat conditions in thefield. This feature also facilitates changing waveguide feed assembliesfor achieving optimum performance at a given frequency.

An actual embodiment of the invention is the commercially available DICOtype AN2M4 dish and feed operative over the frequency range of 10.713.3gHz. with a dish 4 feet in diameter having a focus of 18 inches from thedish surface along the dish axis. The VSWR was less than 1.15 over thisfrequency range.

There has been described a novel waveguide feed for an associatedreflector. It is evident that those skilled in the art may now makenumerous modifications and uses of and departures from the specificembodiment described herein without departing from the inventiveconcepts. Consequently, the invention is to be construed as embracingeach and every novel feature and novel combination of features presentin or possessed by the apparatus and techniques herein disclosed andlimited solely by the spirit and scope of the appended claims.

What is claimed is:

1. Apparatus for radiating electromagnetic energy comprising,

hollow conducting means defining a waveguide closed at one end by meansincluding a conducting plate generally perpendicular to the axis of saidwaveguide and extending beyond the perimeter thereof, said hollowconducting means being formed with slit means defining an apertureclosely adjacent to said conducting plate for exchanging energy betweenthe interior of said waveguide and means external to said waveguideintercepting a beam having an apex embraced by said aperture anddirected away from said waveguide and said conducting plate toward theother end of said waveguide.

said means external to said waveguide comprising means defining areflecting surface having at least one focus embraced by said slitmeans,

said means defining a reflecting surface having means for detachablysecuring said waveguide thereto,

said means for detachably securing including, means defining a reflectorflange permanently attached to said reflector surface,

a plurality of stud means angularly spaced about the waveguide axispermanently secured to said reflector flange each formed with headmeans, and

further comprising means defining a waveguide flange at said other endfor mating relationship with said reflector flange and formed with aplurality of clearing openings angularly spaced about the waveguide axiseach arranged for receiving a corresponding one of said studs wherebywith said waveguide flange seated in mating relationship with saidreflector flange, said studs maintain said flanges in fixed angularrelationship with said heads protruding outside said clearing openings,

locking ring means formed with a plurality of circumferentially slottedopenings each having a clearance portion arranged to coincide with arespective one of said clearing openings when said locking ring means isin an unlock position permitting relative displacement between saidflanges along the waveguide axis rectangular waveguide having at leastopposed broad walls and said slit means defines opposed apertures inrespective ones of said broad-walls oriented with aperture lengthgenerally parallel to said conducting plate, aperture width much lessthan said aperture length and aperture spacing from said conductingplate less than said aperture length.

3. Apparatus for radiating electromagnetic energy in accordance withclaim 2 wherein said rectangular waveguide is dimensioned to propagateenergy over a band centered about a frequency corresponding to apredetermined wavelength,

said aperture length being less than a half and more than a quarter ofsaid predetermined wavelength, said aperture Width being much less thana quarter of said predetermined wavelength.

4. Apparatus for radiating electromagnetic energy in accordance withclaim 3 wherein said aperture length corresponds to substantially 0.4said predetermined wave- Q9 length and said aperture width correspondsto substan tially 0.1 said predetermined wavelength.

5. Apparatus for radiating electromagnetic energy in accordance withclaim 3 wherein said conducting plate is circular and has its center onthe axis of said waveguide.

6. Apparatus for radiating electromagnetic energy in accordance withclaim 1 and further comprising,

rod-like means passing through said conducting plate into said waveguidegenerally parallel to the waveguide axis adjacent to said slit means forreducing reflected energy in said waveguide,

7. Means for detachably securing a waveguide comprising, means defininga first flange formed with an opening embracing said waveguide axis,

a plurality of stud means angularly spaced about the waveguide axispermanently secured to said first flange each formed with head means,

means defining a second flange formed with an opening embracing saidwaveguide axis for mating relationship with said first flange and formedwith a plurality of clearing openings angularly spaced about thewaveguide axis each arranged for receiving a corresponding one of saidstuds whereby with said second flange seated in mating relationship withsaid first flange, said studs maintain said flanges in fixed angularrelationship with said heads protruding outside said clearing openings,

locking ring means formed with a plurality of circumferentially slottedopenings each having a clearance portion arranged to coincide with arespective one of said clearing openings when said locking ring means isin an unlock position permitting relative displacement between saidflanges along the waveguide axis and a locking portion for gripping theunderside of a respective head when said locking ring means is in alocked position preventing relative displacement between said flangesalong the waveguide axis and a locking portion for gripping theunderside of a respective head when said locking ring means is in alocked position preventing relative displacement between said flangesalong the waveguide axis, and

means for securing said locking ring means to said second flange,

said means for securing including means for establishing limitedrelative angular displacement between said locking ring means and saidsecond flange about the waveguide axis between said locking position andsaid unlocked position.

References Cited UNlTED STATES PATENTS 2,775,760 12/1956 Brown et al.343781 2,778,016 1/1957 Chu 34377l 2,907,034- 9/1959 Brown 343781 ELILIEBERMAN, Primary Examiner U.S. Cl. X.R. 343-781

